In next generation multimedia mobile communication systems, which have been actively studied in recent years, there is a demand for a system capable of processing and transmitting a variety of information (e.g., video and radio data) in addition to the early-stage voice service.
Orthogonal frequency division multiplexing (OFDM) is a multiple-subcarrier modulation scheme in which data transmission is achieved by dividing a frequency bandwidth into a plurality of orthogonal subcarriers. The OFDM is one of noticeable core technologies in the next generation multimedia mobile communication systems. Orthogonal frequency division multiple access (OFDMA) provides multi-user multiplexing by combining the OFDM with frequency division multiple access (FDMA) or time division multiple access (TDMA) or code division multiple access (CDMA).
A multiple-input multiple-output (MIMO) system uses multiple transmitting antennas and multiple receiving antennas to improve efficiency of data transmission and reception. A MIMO technology includes spatial diversity and spatial multiplexing. The spatial diversity is a technique in which the multiple transmitting antennas transmit the same data and thus transmission reliability increases. The spatial multiplexing is a technique in which the multiple transmitting antennas simultaneously transmit different data and thus a high speed data can be transmitted without increasing a system bandwidth. The MIMO system has a plurality of independent channels according to the number of transmitting antennas and the number of receiving antennas. Each independent channel can be referred to as a spatial layer or a stream.
In general, a control signal is periodically or event-drivenly transmitted from a base station (BS) to a subscriber station (SS), or from the SS to the BS. The control signal represents a signal that does not include a user signal. Hereinafter, a downlink (DL) represents a transmission from the BS to the SS, and an uplink (UL) represents a transmission from the SS to the BS. An example of UL control signals, there is a channel quality indicator (CQI). In general, the SS periodically transmits the CQI to the BS in order to report channel quality.
The CQI is information required when the BS optimally allocates resources to the SS. The shorter the transmission period of the CQI becomes, the better the channel quality of the service is. However, due to overhead resulted from CQI transmission, there is a limit in reducing the transmission period of the CQI. Further, in the MIMO system, the CQI for each stream may be transmitted, or additional MIMO control information may be transmitted. Therefore, overhead resulted from control information increases more largely.
Accordingly, there is a need for a method for reducing overhead resulted from the periodically transmitted control information such as CQI.